Standards for WLAN technology have been developed by the Institute of Electrical and Electronics Engineers (IEEE) 802.11 specifications. IEEE 802.11a and 802.11b use an unlicensed band at 2.4 GHz or 5 GHz. IEEE 802.11b provides a transmission rate of 11 Mbps and IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g applies Orthogonal Frequency-Division Multiplexing (OFDM) at 2.4 GHz to provide a transmission rate of 54 Mbps. IEEE 802.11n applies Multiple Input Multiple Output (MIMO)-OFDM to provide a transmission rate of 300 Mbps for four spatial streams. IEEE 802.11n supports a channel bandwidth up to 40 MHz to provide a transmission rate of 600 Mbps.
Currently, the IEEE 802.11 of standard, which specifies operation of an unlicensed device in a TV White Space (TVWS) band, is being developed.
A TVWS includes an Ultra High Frequency (UHF) band and a Very High Frequency (VHF) band as a frequency allocated to a broadcast TV and means a frequency band in which an unlicensed device is permitted to be used under the condition that it does not hinder communication of a licensed device operating in a corresponding frequency band. The licensed device may include a TV, a wireless microphone, etc. The licensed device may be called an incumbent user or a primary user.
Operation of all unlicensed devices is permitted in frequency bands of 512 to 608 MHz and 614 to 698 MHz except for a few special cases. However, in frequency bands of 54 to 60 MHz, 76 to 88 MHz, 174 to 216 MHz, and 470 to 512 MHz, communication only between fixed devices is permitted. The fixed devices refer to devices which transmit signals only at a given location. An IEEE 802.11 TVWS terminal refers to an unlicensed device operating using an IEEE 802.11 Media Access Control (MAC) layer and a physical layer (PHY) in a TVWS spectrum.
An unlicensed device which desires to use a TVWS should provide a protection function for a licensed device. Accordingly, the unlicensed device must confirm whether the licensed device occupies a corresponding band before starting signal transmission in the TVWS.
To this end, the unlicensed device should obtain channel list information usable in a corresponding area by accessing a geo-location database through the Internet or a dedicated network. The geo-location database is a database for storing and managing information of registered licensed devices, geo-locations of the licensed devices, and channel use information which dynamically varies over a channel use time.
Alternatively, the unlicensed device may confirm whether a corresponding band is being used by the licensed device by performing spectrum sensing. A spectrum sensing mechanism includes an energy detection scheme and a feature detection scheme. If strength of a signal received in a specific channel is above a prescribed value or if a DTV preamble is detected, the unlicensed device may determine that the licensed device is using the specific channel. If it is determined that the licensed device is being used in a channel immediately adjacent to a currently used channel, the unlicensed device should lower transmission power.
However, there may be unlicensed devices which attempt operation in an unusable channel or are operating in an unusable channel, without conforming to regulations. Accordingly, a method for detecting and then de-enabling such an illegal device is required.